Ceramic armor is typically used for body armor and for the protection of different types of vehicles, such as various types of land vehicles, ships, and aircraft.
Usually, ceramic armor is made of a ceramic tile and composite material as backing. Typically, ceramic tiles are adhesively secured to a substrate then encapsulated in an outer cover. The substrate and cover represent the backing composite material.
The ceramic armor system is then attached to a vehicle by a variety of means or merely placed in a fabric pocket, as in the case of body armor.
The function of the ceramic layer is to break the bullets, while the function of the composite backing is to hold the ceramic in places during the impact and to catch the fragments produced during the impact and dissipate their mechanical energy by a plastic deformation.
A very important characteristic of ceramic component armors is their ability to defeat multiple shots within a relatively small area. The challenge in developing multi-hit ceramic composite armor is to control the damage of the armor structure after the impact in its proximity. While metal armor have inherently this characteristic, that is related to the metal ductility and ability to withstand plastic deformation, in ceramic armor components it must be addressed by an appropriate design of the armor components.
The damage produced in ceramic hard face components by projectile impact can be classified into (1) a comminution zone of highly pulverized material in the shape of a conoid under the incident projectile footprint, (2) radial and circumferential cracks, (3) spalling, through the thickness and lateral directions by reflected tensile pulses, and (4) impact from comminuted fragments.
Crack propagation is arrested at the boundaries of an impacted tile if the web between the tiles in the tile array is properly designed. However, stress wave propagation can occur through the web and into the adjacent tiles and can still damage the adjacent tiles.
As far as the ceramic layer is considered, the most common approach to increase the multi-hit capability of a ceramic composite armor is the use of ceramic tile mosaics. The physical separation between the tiles in the mosaic constitutes a barrier to the propagation of the ceramic damage that occurs during the impact. In this way the area of the ceramic strike face damaged by an impact is limited to the size of the tile or maximum to a portion of two if the impact occurs across the junction.
From the industrial point of view, the drawback of this approach is the increased complexity introduced in the composite manufacturing. During the bonding of the tiles, great care must be used to avoid that an excessive gap between the tiles is introduced. While a minimum gap (0.1-0.3 mm) may be beneficial, an excessive one (0.5 mm or greater) constitute a week point of the ceramic armor to be avoided.
For the above mentioned reasons, the lay-up of mosaic in the construction of composite armor on industrial scale is the most labor intensive production phase. Usually, tiles are aligned manually by trained personnel. The increasing multi-hit requirements are forcing armor designer to adopt more and more mosaics based on small ceramic, like tiles 20 mm×20 mm or 30 mm×30 mm. When using such small tiles, the number of components per square meter increases very rapidly to more than 1000-2000 units.
An additional drawback of ceramic components armor based on mosaics is how to guarantee that in the finished armor every gap between the tiles in below the maximum allowed (usually 0.3/4 mm). The only possibility is to X-ray the entire panel to measure the gap between the tiles. This is a significant expensive measurement.
In order to overcome the above said difficulties, it has been thought to use larger tiles with some discontinuities in their structure. These slots can involve the whole tiles thickness or only part of it and function as breaking barrier to the crack propagation during the impact phase.
In the patent requests EP 1 878 933, WO 2005114089 and GB 2377006 are described different applications of the above said solution.
Unfortunately, this finding did not reveal itself as completely satisfying since it implicates serious manufacturing problems. In fact, ceramic tiles are not easily cut because of their typical hardness.
This is the reason why in literature reference is always made to ceramic carbides the mechanical manufacturing necessity or to the complex forming processes and always regarding ceramic carbides.
Since the market constantly requires strong, low-cost and easily realized armors with high multi-hit properties, it is evident the need to develop ceramic monolithic tiles that do not involve a complex mosaic structure, capable of overcoming the manufacturing problems relevant to the realization to the slots described before.